Transparent touch switching systems for display screens are known in the art. One type of switching system relies upon a change capacitance occuring when the operator applies pressure to a front transparent covering plate to deflect it toward a rear substrate, Penz, U.S. Pat. No. 4,224,615.
Another type of transparent touch switching system relies upon physical engagement of contacts: Fluke 1702A Instrument Controller; Sierracin Transflex TM Membrane Switch.
The present invention employs a different approach and uses a piezoelectric polymer film supported above the screen for selective localized depression towards the screen. The film has transparent flexible conductive coatings on opposite sides thereof for voltage generation in response to depression of the film.
Piezoelectric polymer films are known in the art: Naval Research Reviews, May 1978, Pages 9-11; commercially available from Pennwalt Corporation. Piezoelectric polymer films have been used for input switching systems, but only in keyboard applications: Yoshida et al U.S. Pat. No. 3,935,485; Ohigashi et al U.S. Pat. No. 3,940,637.